Terminating Flexible Cords, Recessed Outlet Boxes and More

Flexible cord terminations

Q: May a properly sized flexible cord with 15-ampere male attachment plugs on both ends be used to supply an optional standby generator for a small business? The cord is intended to plug into a receptacle on the generator and a receptacle on the outside of the building.

A: This method of connecting the generator to the premise-wiring system does not satisfy the Code in at least two instances. First, there must be a manual or automatic transfer switch to connect the generator to the interior wiring. Transfer equipment is required by 702.6.

The flexible cord with attachment caps on both ends does not conform to the requirements in 406.6(B): “Attachment plugs shall be installed so that their prongs, blades, or pins are not energized unless inserted into an energized receptacle.”

Grounding separately derived systems

Q: If I bond the XO terminal of a 480-volt, 3-wire, 3-phase 75 kVa transformer with a 208Y/120-volt secondary to the case of the transformer and install a grounding-electrode conductor from the transformer to the building steel, am I also required to bond the neutral bus in the panel that supplies secondary loads?

A: Where the wiring method from the transformer enclosure to the panel is recognized as an equipment-grounding conductor by 250.118, the answer is no. The neutral bus in the distribution panel must be isolated (insulated) from the panelboard enclosure to prevent a parallel path for neutral current. Part of 250.30(A) contains this statement: “A grounding connection shall not be made to any grounded circuit conductor on the load side of the point of grounding of the separately derived system except as otherwise permitted in this article.” This sentence appears in Exception No. 2: “A system bonding jumper at both the source and the first disconnecting means shall be permitted where doing so does not establish a parallel path for the grounded conductor.”

Where the wiring method between the transformer and panel is in a nonmetallic raceway, the neutral bus in the panelboard may be bonded to the enclosure because a parallel path for neutral current is not established.

Metal extension rings on plastic boxes

Q: Am I permitted to use metal extension rings on plastic boxes where the plastic boxes are recessed in the wall?

A: Boxes that are recessed in combustible walls or ceilings must be provided with plaster rings, extension rings or other devices so that boxes are flush with the surface or extend from there. Metal plaster rings and extension rings are often used for this purpose. The metal extension rings must be grounded.

Part (D) of 250.148 points out that this metal fitting must be grounded: “(D) Nonmetallic Boxes. One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding.” Part (B) of 250.148 requires that the extension ring be individually grounded so that removal of a receptacle, switch, luminaire or other device or equipment does not interfere with or disrupt the grounding continuity.

Working space

Q: The existing 480/277-volt service in an office building is being increased from 800 amperes to 1,400 amperes. A motor-control center and dry-type transformer are on the opposite side of the working space for the new switchboard. With the new switchboard in place, the working space will be about 3 ft., 7 in. Is this adequate? Will the doors have to swing outward and is panic hardware now required on these existing doors?

A: The working space in front of the new switchboard is allowed to be reduced to 3 ft., 6 in., if certain conditions are met. The following is the paragraph that allows this reduction: “Existing Buildings. In existing buildings where electrical equipment is being replaced, condition 2 working clearance shall be permitted between dead-front switchboards, panelboards, or motor control centers located across the aisle from each other where conditions of maintenance and supervision ensure that written procedures have been adopted to prohibit equipment on both sides of the aisle from being open at the same time and qualified persons who are authorized will service the installation.”

There is no relief in 110.26 for the doors. They must swing outward and be equipped with panic bars, pressure plates or latches that open under simple pressure.

GFCI receptacles in a break room

Q: Does the National Electrical Code require GFCI-protected receptacles in an employee break room that contains a sink, refrigerator, coffee maker and microwave oven?

A: A change has been made in 210.8(B)(2) in the 2005 edition in response to proposals requesting clarification of the meaning of a commercial kitchen. The revised wording for 210.8(B)(2) is “Commercial and Institutional Kitchens-for the purposes of this section, a kitchen is an area with a sink and permanent facilities for food preparation and cooking.” In my opinion, a microwave oven is not a permanent appliance for cooking; therefore, GFCI protected receptacles are not required.

Recessed luminaire above a bathtub

Q: Does a recessed lighting fixture installed in an 8-ft. ceiling above a bathtub require GFCI protection? Does the lighting fixture have to be marked “suitable for wet locations”?

A: There is no requirement in the NEC for GFCI protection of the recessed lighting fixture installed above the bathtub.

Only 15- and 20-ampere, 125-volt receptacles are required to be GFCI protected. However, the manufacturer's installation instructions may specify GFCI protection. For this reason, you should read these instructions before the installation of the luminaire (lighting fixture).

I would not classify the ceiling above a bathtub as a wet location, but the ceiling area above the tub should be classified as a damp location. Under this classification, a damp or wet location lighting fixture is acceptable.

Protecting threads on RMC

Q: Does the NEC permit the use of pipe dope or Teflon tape on field cut threads on rigid metal conduit (RMC) installed in the earth?

A: I am not sure that pipe dope and/or Teflon tape used on field cut threads provide the grounding continuity required. Here are some excerpts from 300.6 that deal with this problem. “(A) ... where corrosion protection is necessary and the conduit is threaded in the field, the threads shall be coated with an approved electrically conductive, corrosion-resistant compound.”

Here are the requirements for direct burial: “300.6(A)(3) In Concrete or in Direct Contact with the Earth. Ferrous metal raceways, cable armor, boxes, cable sheathing, cabinets elbows, couplings, nipples, fittings, supports, and support hardware shall be permitted to be installed in concrete or in direct contact with the earth, or in areas subject to severe corrosive influences where made of material approved for the condition, or where provided with corrosion protection approved for the condition.” Notice the word “approved” is used in both quoted parts of 300.6(A). Therefore, you should check with the authority having jurisdiction for types of anticorrosion compounds that are electrically conductive and acceptable.

Recessed outlet box for receptacles

Q: The vanity receptacle outlet box is recessed one-half inch because of the installation of a mirror. Must an extension ring be installed where the wall surface (mirror) is noncombustible?

A: Yes, a plaster ring or box extension must be provided so that the box is not recessed more than one-fourth of an inch. The extension ring should bring the box edges to the surface of the mirror or not be recessed more than one-fourth of an inch. This requirement is in 314.20.

Metal lighting poles used as raceways

Q: Under what conditions may 20-ft. metal light poles at a used car lot be used as a raceway? Are type THHN copper conductors suitable for use in a lighting pole?

A: A metal lighting pole may be used as a raceway provided that it has a hand hole that is not smaller than 2 in. by 4 in. and has a rain-tight cover. This requirement does not apply to a hinged pole. (See 410.15(B)(1) and Exception No. 2).

Type THHN conductor insulation is suitable for use in dry or damp locations only, and electrical installations located outdoors are considered wet locations as indicated by the definition in Article 100; therefore, type THHN insulated conductors are not acceptable. Some suitable substitutions are Types THHW, THW or THWN insulations.

Connectors for aluminum armored cable

Q: Are there any restrictions on the use of armored cable connectors on Aluminum Armored Cable that are not covered in the National Electrical Code?

A: Yes there are some restrictions on the use and types of connectors that may be used with this product. In addition to the rules in the NEC, aluminum-sheath armored cable cannot be used on direct-current systems, and direct-bearing set-screw connectors cannot be used because the set-screw, when tightened, can penetrate the armor and make contact with a contained conductor. EC

FLACH, a regular contributing Code editor, is a former chief electrical inspector for New Orleans. He can be reached at 504.734.1720.